Bootsie the cat and Mr. Bates, the Pomeranian-Chihuahua mix, are just two among thousands of metro-Phoenix shelter animals looking for homes this weekend as part of Maddie's Pet Adoption Days, the nation's largest free pet-adoption event.

Valley residents can adopt a cat or dog, for free, at 40 locations in Maricopa County on Saturday and Sunday, May 31 and June 1. Take a look at the list of Maricopa County pets up for adoption on the Maddie's Fund website to find the pet that's right for you.

The event is part of a nationwide pet-adoption event that will include more than 200 animal shelters in nearly 600 cities across the country coordinated and financed by Maddie's Fund, a charitable foundation that helps save homeless and sheltered animals.

For the first time in Arizona, Maddie's Fund will be working with 12 Maricopa County animal-welfare organizations, including the Arizona Animal Welfare League, HALO Animal Rescue and the Arizona Humane Society, with the goal of finding homes for at least 1,500 animals this weekend.

"People need to come down and look at what's available, we will still do a screening process, but it's a good opportunity," said Melissa Gable, public-information officer for Maricopa County Animal Care and Control. "If you've been thinking about adopting ,now is the time do it because there are going to be a lot of adorable dogs and cats that need help."

In 2013, Maricopa County animal-welfare organizations sheltered more than 80,000 animals, Gable said. Although the number of sheltered animals is decreasing every year, thanks in part to spay and neuter efforts, Maricopa County Animal Care and Control still takes in more than 100 animals every day, she said.

"There's not enough room. On a good day, we adopt out 100 animals, but that's not every single day, so it's a constant scramble to try and find space," Gable said. "We are really fortunate to have Maddie's step up and help us."

Maddie's Fund has earmarked $10 million to help such programs around the country by donating as much as $2,000 per animal to pay for spaying and neutering, vaccinations and other medical expenses so that people can adopt the animals for free.

"Our goal is to try and get the shelters empty so that we can again fill them right back up with animals that are coming in. And it also gives us a chance to remind the public that shelter pets are wonderful animals," Gable said.

Details: Various hours Saturday, May 31, and Sunday, June 1. For locations and pet information, visit adopt.maddiesfund.org.

Correction: A previous version of this story stated that guinea pigs, hamsters and other small animals also will be free for adoption. The Arizona Humane Society is considering free adoptions for small animals, but at this time, regular adoption fees will only be waived for cats and dogs.